The use of solenoid operated two-way valves in internal combustion engines is well known in the art and, more particularly, valves of this type are known to be used to control the flow of fuel into a timing chamber of an electronically controlled unit injector to permit control of both the quantity and timing of fuel injected into the internal combustion engine.
U.S. Pat. No. 4,431,160 issued to Burt et al. discloses an electrically operated valve for use in unit injectors. The '160 valve includes a cup shaped valve element universally mounted on a stem operator for movement between open and closed positions. A spring element biases the operator toward the valve open position. An armature mounted on the stem operator opposite the valve element is selectively attracted toward the stator of a solenoid to cause the valve element to move to its closed position whenever the solenoid coil is energized. Valves of the type disclosed in the '160 patent are required to operate at very high speed (fully opened and closed in 2.5 seconds) and must operate to block fluid at very high pressure (25-30,000 psi). To achieve this very high speed, the '160 cup shaped valve element must be arranged close to the valve seat as possible while providing adequate flow volume capacity. Such requirements necessitate extremely accurate positioning of the valve element relative to its valve seal.
When closed, valves of the type disclosed in '160 patent must create a very tight seal and thus the valve element is mounted by a self-aligning assembly. To allow for the accurate adjustment noted above, the self-aligning assembly includes a nut threadingly engaged with the stem operator so as to properly position the valve element. The nut includes an upper spherically shaped surface which is in constant contact with a conically shaped lower surface of the cup shaped valve element. The axial spacing between the valve element and the valve seat defines the stroke length of the valve and it is critical that this spacing be maintained at a predetermined optimum value. Fluctuation in this spacing of as little as 0.002 inches can affect the metering and timing of the injector and may eventually result in unacceptable performance of the injector, necessitating expensive repair. This fluctuation arises due to repeated impacts caused by reciprocation of the valve element between its open and closed positions. Therefore, it is essential that the nut, which retains the cup-shaped valve element of the valve, be fixed in its pre-determined optimum position and that this position be maintained throughout the life of the injector. In the above mentioned U.S. Pat. No. 4,431,160, it is the internal threads which are relied upon to act on the nut to hold the nut in place. This, however, has not been found to be reliable due to the above mentioned constant reciprocation of the cap and nut. During this constant reciprocation, the valve will vibrate, which, in turn, will cause the adjustment nut to slip or rotate, thereby deviating from the preset optimum position which may result in failure of the valve and costly repairs.
In an attempt to overcome the above noted shortcomings, U.S Pat. No. 4,905,960 issued to Barnhart et al. discloses a valve stroke adjustment locking mechanism comprising a valve seat having an axially extending bore therethrough and a seating surface, as shown in FIG. 6. A valve operator is provided having an elongated member which is reciprocable between a first open position and a second closed position. The elongated member includes a threaded end portion which extends from the valve seat for accommodating a valve assembly which is provided with a top portion forming a sealing face and a bottom portion having a central opening adapted to receive the threaded end portion of the elongated member. A closed end nut threadingly engages the threaded end portion of the elongated member and contacts the valve assembly for positioning the sealing surface at a predetermined spacing from the seating surface. A transverse hole is then electromechanically discharge machined transversely through the closed end nut and the threaded end portion of said piston member and a pressure fit pin is forced into the hole to rigidly fix the closed end nut relative to the elongated member in order to maintain the predetermined spacing without forming any paths of leakage. However, this valve requires a threaded joint and loctite process for attaching the nut on the high pressure side of the valve. Further, the valve stroke cannot be readily adjusted nor can the assembly be disassembled after the pin has been press fit therein.
Testing of this design has shown adjusting nut retaining torque to be a function of fluid pressure where retaining torque deterioration becomes more pronounced as fluid pressure is increased. Locating the adjustment nut in the high pressure area is the primary cause of the loose nut problem encountered on this prior art design.
It is evident that here is a need for a simplified fastening and adjustment mechanism which will both accurately and reliably position a fluid valve closure element in a predetermined optimum position, and do so without resulting in any leakage of fluid from within the assembly. Furthermore, there is a need for a fastening mechanism which will provide for easier construction of a solenoid valve assembly resulting in a lower cost of manufacture.